The present invention relates to a torque detecting apparatus comprising, for each of an input shaft and an output shaft that are connected with a torsion bar, a rotor; a plurality of targets provided on the rotor so that a region to be detected changes periodically and continuously with rotation of the rotor; and one or a plurality of detecting means for detecting regions of the targets; whereby detecting a torque applied to the input shaft, based on a difference between the regions detected by the detecting means resulting from twist of the torsion bar, and also relates to a steering apparatus for driving an electric motor based on the result of detection of the torque detecting apparatus so as to generate a steering assist force.
There is a type of steering apparatus for automobile, which assists steering by driving the electric motor so as to reduce the driver""s load. This steering apparatus comprises an input shaft connected to a steering wheel; an output shaft connected to a steering control wheel through a pinion and a rack; and a torsion bar connecting the input shaft and output shaft together, detects a steering torque applied to the input shaft with a detecting apparatus based on twist generated on the torsion bar, and drives and controls the steering assist electric motor interlocked with the output shaft, based on the steering torque detected by the torque detecting apparatus.
FIG. 1 is a schematic view illustrating schematically an example of the structures of essential portions of a torque detecting apparatus according to a proposal made in Japanese Patent Application Laid-Open No. 2000-352502 (U.S. patent application Ser. No. 09/719003) filed by the present applicant. FIG. 1 shows an application of this torque detecting apparatus to a steering apparatus, wherein, for example, eight protruding objects (targets) 7 formed of a magnetic material are provided at equal intervals and at a predetermined angle of inclination along a circumferential surface of an intermediate portion (rotor) 6 of an upper shaft (input shaft) 23 of a steering shaft whose upper end is connected to a steering wheel 4 and lower end is connected to a torsion bar 5. Moreover, in order to detect the approaching position of the protruding object 7 that moves in the axial direction of the upper shaft 23 upon rotation of the upper shaft 23, an MR sensor 1 (magneto-resistance effect element, that is detecting means) is provided parallel to the intermediate portion 6 with an appropriate space therebetween and fixed to an immovable portion of the body of vehicle.
The upper end of a lower shaft (output shaft) 18 of the steering shaft is connected to the torsion bar 5, and the lower end thereof is connected to a pinion 10. Like the upper shaft 23, eight protruding objects (targets) 9 formed of magnetic material are provided at equal intervals and at a predetermined angle of inclination along a circumferential surface of an intermediate portion (rotor) 8 of the lower shaft 18. Moreover, in order to detect the approaching position of the protruding object 9 that moves in the axial direction of the lower shaft 18 upon rotation of the lower shaft 18, an MR sensor 2 (magneto-resistance effect element, that is detecting means) is provided parallel to the lower shaft 18 with an appropriate space therebetween and fixed to an immovable portion of the body of vehicle.
The MR sensor 1 incorporates therein sensors 1A and 1B whose electric angle difference is 180xc2x0 (i.e., for detecting the approaching positions of adjacent different protruding objects 7) so as to construct a dual system, and detection signals V1A and V1B indicating the approaching positions of the protruding objects 7 detected by the sensors 1A and 1B are respectively supplied to a calculating unit 3.
The MR sensor 2 incorporates therein sensors 2A and 2B whose electric angle difference is 180xc2x0 (i.e., for detecting the approaching positions of adjacent different protruding objects 9) so as to construct a dual system, and detection signals V2A and V2B indicating the approaching positions of the protruding objects 9 detected by the sensors 2A and 2B are respectively supplied to the calculating unit 3.
The MR sensors 1 and 2 are provided so that the detection signals V1A and V2A are in phase and the detection signals V1B and V2B are in phase in a condition where no steering torque is applied to the steering wheel 4 and the torsion bar 5 is not twisted.
The twist angle of the torsion bar 5 is at most several degrees, and the calculating unit 3 calculates a steering torque, based on the difference between the detection signals V1A and V2A or between the detection signals V1B and V2B, and outputs the torque signal.
In the torque detecting apparatus having such a structure, whenever the upper shaft 23 and the lower shaft 18 rotate 45xc2x0, the protruding objects 7 and 9 closest to the detection faces of the respective sensors 1A, 1B and sensors 2A, 2B reciprocate in the axial direction of the upper shaft 23 and lower shaft 18. It is possible to arrange the positions of the protruding objects 7 and 9 closest to the detection faces of the respective sensors 1A, 1B and sensors 2A, 2B, in the axial direction of the upper shaft 23 and lower shaft 18, to correspond to the rotational angles of the upper shaft 23 and lower shaft 18.
Therefore, if the detection signals of the sensors 1A, 1B and sensors 2A, 2B are set to have a linear relation with every 45xc2x0 rotational angle of the upper shaft 23 and lower shaft 18, it is possible to detect the rotational angles of the upper shaft 23 and lower shaft 18 based on the respective detection signals of the sensors 1A, 1B and sensors 2A, 2B by using counting of the number of times of up and down in the detection signals of the sensors 1A, 1B and sensors 2A, 2B. In addition, it is also possible to discriminate whether the sensors 1A, 1B and sensors 2A, 2B have detected the approaching positions of the respective protruding objects 7 and 9.
For example, in the case where the detection signals of the sensors 1A, 1B and sensors 2A, 2B are set to have a similar relation with the rotational angle (steering angle) of the upper shaft 23 and lower shaft 18, when the upper shaft 23 and lower shaft 18 are rotated, the detection signals of the sensors 1A, 1B and sensors 2A, 2B show voltage waveforms of a cycle of 45xc2x0, and the rotational angles of the upper shaft 23 and lower shaft 18 can be detected by the detection signals of the sensors 1A, 1B and sensors 2A, 2B, respectively.
Here, if a steering torque has been applied to the steering wheel 4 and the torsion bar 5 has a twist angle, the detection signals of the sensors 1A and 2A and the detection signals of the sensors 1B and 2B have a voltage difference xcex94V according to the twist angle, and therefore it is possible to obtain the twist angle by calculating the voltage difference xcex94V with the calculating unit 3 and to output a torque signal representing the steering torque.
The above-described torque detecting apparatus is constructed by providing the rotor 6 on the upper shaft 23 of the steering shaft as an intermediate portion thereof and providing the rotor 8 on the lower shaft 18 as an intermediate portion thereof, but it is difficult to provide the rotors 6 and 8 by precisely keeping a coaxial relation between their rotation axes and the upper shaft 23 and lower shaft 18, and if their relation is illustrated in an emphasized manner, as shown in FIG. 2, the rotation axes of the rotors 6 and 8 are mutually deflected.
Therefore, the positional relation between the MR sensor 1 and the protruding objects 7 and the positional relation between the MR sensor 2 and the protruding objects 9 are not the same depending on the rotations of the rotor 6 and rotor 8, and, if the detection signals of the respective sensors are illustrated in an emphasized manner, as shown in FIG. 3, rotational deflection drawing like a sine wave is generated entirely during one rotation of the rotors 6 and 8, resulting in a problem that an accurate steering torque can not be detected.
Note that, in FIG. 3, Pn and Bn represent the detection signal""s peak value and bottom value, respectively.
The present invention has been made with the aim of solving the problems, and it is an object of the first and second inventions to provide a torque detecting apparatus capable of restraining the influence of rotational deflection and detecting a more accurate steering torque.
It is an object of the third invention to provide a steering apparatus comprising a torque detecting apparatus according to the first or second invention.
A torque detecting apparatus according to the first invention is a torque detecting apparatus comprising for each of an input shaft and an output shaft that are connected with a torsion bar: a rotor; a plurality of targets provided on the rotor so that a region to be detected changes periodically and continuously with rotation of the rotor; and one or a plurality of detecting means for detecting regions of the targets, whereby detecting a torque applied to the input shaft, based on a difference between the regions detected by the detecting means resulting from twist generated on the torsion bar, and is characterized by comprising: discriminating means for discriminating the targets individually based on the regions detected by the detecting means; correction amount calculating means for calculating a correction amount for each of the targets so as to correct the regions detected by the detecting means, based on maximum values or minimum values of signals indicating the regions of each of the targets detected by the detecting means, upon one rotation of the rotors; storing means for storing the correction amounts calculated by the correction amount calculating means; and correcting means for correcting detected regions upon detection of the regions by the detecting means, based on the correction amounts stored in the storing means for the targets discriminated by the discriminating means, wherein the torque applied to the input shaft is detected based on the regions corrected by the correcting means.
In this torque detecting apparatus, each of the input shaft and the output shaft that are connected with the torsion bar is provided with a rotor, and a plurality of targets are provided on the rotor so that a region to be detected changes periodically and continuously with rotation of the rotor. One or a plurality of detecting means detect the approaching regions of the targets, and detect a torque applied to the input shaft, based on a difference between the regions detected by the detecting means resulting from twist generated on the torsion bar.
The discriminating means discriminates the targets individually based on the regions detected by the detecting means, and the correction amount calculating means calculates a correction amount for each of the targets so as to correct the regions detected by the detecting means, based on maximum values or minimum values of signals indicating the regions of each of the targets detected by the detecting means, upon one rotation of the rotors.
The storing means stores the correction amounts calculated by the correction amount calculating means, and the correcting means corrects detected regions upon detection of the regions by the detecting means, based on the correction amounts stored in the storing means for the targets discriminated by the discriminating means, so that the torque applied to the input shaft is detected based on the regions corrected by the correcting means.
Accordingly, it is possible to realize a torque detecting apparatus capable of restraining the influence of rotational deflection and detecting a more accurate steering torque.
A torque detecting apparatus according to the second invention is a torque detecting apparatus comprising for each of an input shaft and an output shaft that are connected with a torsion bar: a rotor; a plurality of targets provided on the rotor so that a region to be detected changes periodically and continuously with rotation of the rotor; and one or a plurality of detecting means for detecting regions of the targets, whereby detecting a torque applied to the input shaft, based on a difference between the regions detected by the detecting means resulting from twist generated on the torsion bar, and is characterized by comprising: storing means for storing a predetermined correction amount for each of the targets so as to correct the regions detected by the detecting means; discriminating means for discriminating the targets individually based on the regions detected by the detecting means; and correcting means for correcting detected regions upon detection of the regions by the detecting means, based on the correction amounts stored in the storing means for the targets discriminated by the discriminating means, wherein the torque applied to the input shaft is detected based on the regions corrected by the correcting means.
In this torque detecting apparatus, each of the input shaft and output shaft that are connected with the torsion bar has a rotor, and a plurality of targets are provided on the rotor so that a region to be detected changes periodically and continuously with rotation of the rotor. One or a plurality of detecting means detect the approaching regions of the targets, whereby detecting a torque applied to the input shaft, based on a difference between the regions detected by the detecting means resulting from twist generated on the torsion bar.
The storing means stores a predetermined correction amount for each of the targets so as to correct the regions detected by the detecting means, and the discriminating means discriminates the targets individually based on the regions detected by the detecting means. Upon detection of the regions by the detecting means, the correcting means corrects the detected regions based on the correction amounts stored in the storing means for the targets discriminated by the discriminating means, and the torque applied to the input shaft is detected based on the regions corrected by the correcting means.
Accordingly, it is possible to realize a torque detecting apparatus capable of restraining the influence of rotational deflection and detecting a more accurate steering torque.
A steering apparatus according to the third invention is characterized by comprising: an input shaft connected to a steering wheel; a steering assist electric motor which is driven and controlled based on a steering torque applied to the steering wheel; an output shaft interlocked with the electric motor; a torsion bar connecting the input shaft and the output shaft together; and the torque detecting apparatus as set forth in claim 1 or 2 for detecting a steering torque applied to the input shaft, wherein steering is assisted based on the steering torque detected by the torque detecting apparatus.
In this steering apparatus, the input shaft is connected to the steering wheel, the steering assist electric motor is driven and controlled based on the steering torque applied to the steering wheel, and the output shaft is interlocked with the electric motor. The torsion bar connects the input shaft and the output shaft together, the torque detecting apparatus as set forth in claim 1 or 2 detects the steering torque applied to the input shaft, and steering is assisted based on the steering torque detected by the torque detecting apparatus.
Accordingly, it is possible to realize a steering apparatus comprising a torque detecting apparatus capable of restraining the influence of rotational deflection and detecting a more accurate steering torque.